Direct Fabrication of Strong Basic Sites on Ordered Nanoporous Materials: Exploring the Possibility of Metal–Organic Frameworks
作者:Wei Liu、Li Zhu、Yao Jiang、Xiao-Qin Liu、Lin-Bing Sun
DOI:10.1021/acs.chemmater.7b05102
日期:2018.3.13
Heterogeneous strong base catalysts possessing ordered nanoporous structure are highly expected due to their high activity and shape selectivity in diverse reactions. However, their fabrication remains a great challenge because quite high temperatures (600–700 °C) are compulsory for the generation of strong basicity on conventional ordered nanoporous materials (i.e., zeolites and mesoporous silicas). Here, we report for the first time direct fabrication of strong basic sites on metal–organic frameworks (MOFs) by using guest–host redox (GHR) interaction between base precursors and low-valence metal centers (e.g., Cr3+), which breaks the tradition of thermo-induced decomposition of base precursors. It is fascinating that base precursor KNO3 can be converted to strong basic species on MIL-53(Cr) at 300 °C, which is much lower than that on zeolite Y (700 °C) and mesoporous silica SBA-15 (600 °C). The resultant solid base exhibits strong basicity, ordered nanoporous structure, and high activity and shape selectivity in base-catalyzed reactions.
具有有序纳米孔结构的异质强碱催化剂因其在大范围反应中的高活性和形状选择性而备受期待。然而,它们的制备仍然是一个巨大的挑战,因为在传统的有序纳米孔材料(如沸石和介孔硅)上生成强碱基团需要极高的温度(600-700°C)。在这里,我们首次报道了通过碱前体和低价金属中心(例如Cr3+)之间的客-主氧化还原(GHR)相互作用,直接在金属有机框架(MOFs)上制备强碱位点,打破了传统的热引发碱前体分解方式。令人着迷的是,碱前体KNO3可以在300°C下转化为MIL-53(Cr)上的强碱物种,远低于沸石Y(700°C)和介孔硅SBA-15(600°C)的温度。所得固体碱展现出强碱度、有序纳米孔结构,以及在碱催化反应中的高活性和形状选择性。